Field of the Invention
The present invention relates to an ultrasonic wave transmitting unit or reception unit, a sheet determination apparatus, and an image forming apparatus.
Description of the Related Art
Image forming apparatuses such as multi-function printers and laser printers use an ultrasonic wave sensor to determine the type of a sheet inside of the image forming apparatus and set image formation conditions such as transfer conditions and fixing conditions according to the determination result. Incidentally, there are cases where ultrasonic waves transmitted from a transmission unit are reflected multiple times and received by a reception unit. Reflection can occur due to a sheet, and also due to members in the periphery of the transmission unit and the reception unit, such as conveyance rollers and conveyance guides for conveying the sheet.
Japanese Patent Laid-Open No. 2001-351141 proposes attaching sonic wave guides by which sonic waves converge respectively at a wave transmitter and at a wave receiver. Japanese Patent Laid-Open No. 2010-018432 proposes determining the length of guides based on the wavelength of the ultrasonic waves so as to stabilize the output of ultrasonic waves that have passed through a recording medium.
Incidentally, there are cases where the ultrasonic wave sensor is arranged at a position at which a user can touch it with his or her fingers. Since an ultrasonic wave sensor transmits and receives ultrasonic waves due to a vibration member vibrating, if the vibration member is touched by a user, it cannot operate normally. Sometimes there are also cases where the ultrasonic wave sensor malfunctions.